Wall St. mixed, Apple impresses and Twitter disappoints

(Reuters) - U.S. stocks were mixed on Tuesday as Federal Reserve policymakers kicked off a two-day interest rate meeting and investors braced for quarterly scorecards from Apple and Twitter.

Choppy stock trading followed a recent rally to consecutive record highs on the S&P 500 that has stretched price-to-earnings multiples to levels that some investors say presumes that companies will beat second-quarter estimates.

Caterpillar's <CAT.N> shares jumped 5.16 percent to touch a year high after quarterly earnings beat expectations.

The Federal Reserve began a two-day meeting and while it is not expected to raise U.S. interest rates, investors will be watching for hints about when the U.S. central bank might make a move.

A set of strong economic data, including Tuesday's housing report, could strengthen the case for the Fed to raise rates earlier than the market anticipates.

"The real thing I'm going to be looking for is, is there a tip of the hat to a potential rate increase in September?," said Brad McMillan, chief investment officer at Commonwealth Financial Network.

The Dow Jones industrial average <.DJI> dipped 0.1 percent to end at 18,473.75 and the S&P 500 <.SPX> edged up 0.03 percent to 2,169.18 after spending much of the day at a loss. The Nasdaq Composite <.IXIC> added 0.24 percent to 5,110.05.

After investors shrugged off Britain's unexpected vote in late June to leave the European Union, the S&P 500 rallied and is up 6 percent year to date.

Almost a third of the way into second-quarter reports, S&P 500 companies overall are expected to see earnings dip 3.5 percent, not as bad as the 4.5 percent dip predicted at the start of the month, according to Thomson Reuters I/B/E/S.

Shares of Apple <AAPL.O>, the world's largest publicly traded company, dipped 0.69 percent ahead of its quarterly report after the bell.

In extended trade, Apple surged 4 percent after the company reported more iPhone sales than expected for the June quarter.

Twitter <TWTR.N> slumped 9 percent after the social network reported its slowest quarterly revenue growth since going public in 2013.

Earlier, McDonald's <MCD.N> sank 4.46 percent after reporting worse-than-expected quarterly sales at established U.S. restaurants. The stock weighed the most on the Dow.